Sulfur is generally burned with dry air in a combustion chamber in the production of sulfur dioxide, obtaining a gas of 80% V/V of nitrogen, 18% V/V of SO2, the rest being oxygen and inert gases. This gas is then liquefied at a temperature of −50° C. at a pressure of 0.8 bar. Greater pressure is required to liquefy this product at a higher temperature. The SO2 recovery efficiency achieved through the liquefication of this gas is approximately 75%. The rest of the non-liquefied SO2 gas, excess oxygen not burned and inert gases must be eliminated from the process line. If this mix is discharged into the atmosphere, contamination is heavy and a costly neutralization procedure is required to reduce contamination.